The present invention relates to a method for discharging gas reduced iron from a vertical furnace at a high temperature, effecting component adjustment so as to render the reduced iron to be in a condition desirable for use in succeeding processes, and discharging the reduced iron into the exterior atmosphere after cooling the same, and an apparatus for carrying out the above method.
Grannular iron oxide, such as, for example, pellets of 10 - 30 mm in diameter which are formed by shaping powdered iron ore substantially of uniform size, pellets or briquettes formed from the mixture of powdered iron ore and collected dust (mainly of iron oxide powder), or grannular iron ore obtained by crushing a mass of ore and sizing them into a size ranging from about 10 to about 30 mm, is charged to the top of the vertical furnace. On the other hand, reducing gas held at a predetermined temperature is introduced into the vertical furnace at the bottom thereof, so that the reducing gas flows upwardly in the furnace in counter-flow to the iron oxide in contact therewith thereby effecting reduction of the iron.
The above described reduced iron descends in the vertical furnace while the gas reduction proceeds and is discharged from the bottom of the furnace and received in cooling receptacles. After cooling, the reduced iron is used as a raw material for the manufacture of steel.
On the other hand, the reducing gas blown into the furnace is discharged from the top of the furnace after is has been used in gas reduction of the iron oxide during its rising through the furnace. The thus discharged waste gas is processed in a gas recirculating system so that the water component and carbon dioxide are removed therefrom. Alternately, a part of the carbon dioxide is maintained therein, and fuel is newly supplied to the thus processed gas so as to effect denaturation thereof and the thus denatured gas is supplied to the vertical furnace for the gas reduction of the iron oxide. It may also be used in heat exchange with the fuel and other medium in the recirculation system or it is cooled by the other medium to make a low temperature reducing gas so that it is used as a cooling medium for the reduced iron in the vertical furnace. To effect the above processes, various methods and apparatuses are well known.
As to the means for producing the reducing gas used in the gas reduction of iron ore, the method of obtaining high temperature reducing gas by partially oxidizing heavy oil, natural gas and other hydrocarbon fuels in the presence of oxygen, the method of improving the nature of the above described fuel by water vapor in the presence of a catalyst (steam reforming), or the method of improving the nature of the above described fuel by using CO.sub.2 as a source of oxygen in the presence of a catalyst are suitable.
In producing the above described reducing gas, it is preferred that the amount of impurities, particularly, the amount of sulfur, contained in the fuel are low. However, since the amount of production of such a high quality fuel is limited and it is expensive, fuel having a high content of sulfur must be used.
When a reducing gas is produced from a sulfur containing fuel, such as, a heavy oil containing 0.2% of sulfur, and the reducing gas is used in reducing iron oxide, the content of sulfur in the reduced iron reaches 0.05 - 0.1%, thereby remarkably deteriorating the quality of the reduced iron and making the succeeding processes very complicated and troublesome.
In the catalyst contact process, when the sulfur content of the fuel and other medium is more than 0.001%, the ability of the catalyst used is severely deteriorated so that frequent exchange of the catalyst is required. Therefore, it is desired to desulfurize the fuel prior to the production of the reducing gas. However, the provision of desulfurizing equipment only for the desulfurization of the fuel makes the production cost of the reduced iron very high.